Regulated radio frequency operated high voltage power supply



July I7, 1959 1 M. BERNBAUM 2,894,195

REGULATED RADIO FREQUENCY AOPERATED HIGH VOLTAGE POWER SUPPLY Original Filed Oct. 20. 1955 vso 3 l g Ill ql-U "I N LO ..-g INVENTOR.

6 6 LESTER M. BERNBAUM Q' l g BY 'ATTORNYS' United States Patent REGULATED RA'DIO FREQUENCY OPERATED HIGHVOLTAGE POWER SUPPLY Lester M. Bernbaum, Levittown, Pa.

Original application October 20, 1953, Serial No. 387,329. -Divided and this application October 31, 1955, Serial No. v544,095

. 5 Claims. (Cl. 321-18) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used |by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

'Ihe present invention relates to a regulated radio frequency operated high voltage power supply and more particularly to a high voltage supply which is highly stabilized.

Some present high voltage power supplies for cathode ray tubes and the like use an oscillator operating at a plate potential of the order of 500 volts generating a few watts of power at a frequency that may be several hundred kilocycles. A resonant load circuit is then coupled to the oscillator tank circuit and in this manner it is possible to obtain a high radio frequency voltage by resonance. This voltage is stepped up by a suitable transformer to a sutliciently high voltage necessary in the cathode ray tube and the output of this is rectified either by a halfwave or by a voltage multiplying circuit to give a very high D.C. potential. Such arrangements usually do not provide a stabilization circuit for exercising close control of the output. With the development of modern precision electronic devices vfor use in locating targets, for example, the need for highly stabilized voltage sources has steadily risen.

The present arrangement proposes to modify the type of high voltage power supply described above so as to produce a highly stabilized and closely regulated voltage source for use in cathode ray tubes and the like. This is accomplished in the present arrangement by using a feedback circuit consisting of a pentode and two triodes which closely regulate the pickoif of the screen grid in the pentode of the oscillator circuit. As will be seen below, this arrangement provides a circuit which delivers a voltage closely regulated and unvarying for use in highly specialized equipment requiring such closely regulated voltages.

This Vapplication is a division of application Serial No. 387,329 led October 20, 1953, for Target indicating Mechanism, now Patent No. 2,866,967.

An object of the present invention is the provision of a high voltage power supply which is capable of delivering a voltage at a closely regulated value.

Another object is to provide a regulated ratio frequency operated high voltage power supply for a cathode ray tube which is of compact and safe construction since it employs low value capacitors for filtering and delivers only a limited amount of power.

A further object of the invention is the provision of a regulated radio frequency operated high voltage power supply for a cathode ray tube in which stabilization of the oscillator circuit is accomplished by controlling the screen voltage of the tube oscillator.

Still another object is to provide a closely regulated radio frequency oscillator utilizing a vacuum tube having a screen grid, the voltage of which is automatically regulated in accordance with the output of said oscillator to closely regulate the voltage output of said oscillator.

A final object of the present invention is the provision of a voltage regulated radio frequency operated high voltage power supply for a cathode ray tube utilizing a radio frequency oscillator and provided with screen voltage control for exercising and permitting stabilization of the output voltage.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawing which illustrates a preferred embodiment of this invention.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts, there is shown a high voltage power supply employing a radio frequency oscillator V29 which may be operated at about 235 kilocycles per second. Plus 320 volts are applied to the plate of V29, the oscillator, through resistance R402 and the primary coil of transformer T401. The suppressor grid of tube V29 is tied to its cathode in accordance with conventional practice. Transformer T401 in the plate circuit of V29 permits output to be delivered to the high voltage power supply through the positive pulses produced at the plate of V29. Primary pulses across the primary of T401 shock the secondary of T401 into oscillations which provide an RF frequency for rectication. A tickler winding shown at the top of the transform-er together with capacitor C401 provides positive feed back to the grid of oscillator V29. The grid of oscillator V29 is provided with a grid resistor R401 and capacitor C402 to permit the grid to be operated at Class C.

The frequency of oscillation is determined chiey by the resonant frequency of the secondary winding of T401. The natural circuit capacitances that tune this winding include the distributed capacitance of the winding, the capacitance of the rectifying tubes V30 and V31 and the stray wiring capacitance. The primary winding is tuned by fixed capacitor C409 to approximate the resonant frequency of the secondary. As indicated hereinbefore, the third winding of the transformer located at the end of the secondary winding opposite from the end occupied by the primary and shown lat the top of the figure is loosely coupled to the secondary and provides good excitation for oscillator tube V29.

Filament voltage is supplied to rectifying tubes V30 and V31 by two additional single turns XZ and Y and the secondary lead coupled to the secondary winding of T401.

Half wave rectification is produced as follows: On the negative swing at the lament of tube V30, tube V30 conducts through R403 and through the bleeder circuit comprising resistors R405, R404, R406, potentiometer R407 and resistor R408 to ground. Filtering action is pro-vided by filter resistor R403 and capacitors C404 and C405.

Halfwave rectication is provided on the positive swing by conduction of tube V31, from tap 201, through the cathode ray tube (not illustrated) to ground. The

path of electron flow comes from [ground through center `tap 202, through the cathode (not illustrated) of the cathode ray tube, to the intensifier ring (not illustrated), thence from tap 201 to the lament of V31, through the secondary of T401 and back to ground. C406 is a iilter capacitor. In this manner positive 1500 volts, on tap 201, and negative 1500 volts, on tap 203, are obtained. Hence, a full wave voltage doubler arrangement is essentially provided, the direct current high voltage appearing between output Iterminals 201-203 being substantially twice the peak voltage of the high voltage 'secondary winding of transformer T401. The stabilizing circuit for controlling the screen current of oscillator V29 is provided by inverter V33b, pentode control amplifier V32 and a variable impedance stage V33a in series with Ithe screen grid of oscillator V29. A portion of the output voltage from the high voltage negative supply tapped from potentiometer R407 in the high voltage negative supply bleeder, is impressed in the grid of V336 and compared with a constant regulated minus 75 volts on the cathode of triode inverter V331). The plate load of V33b is developed across R410, while C408 provides high frequency by-pass. The inverted output at the plate of V33b is applied to the grid of the control amplifier V32.. Plate voltage to tube V32 is provided from the 32() volt supply through plate load resistor R409 to the plate of that tube. Screen and plate of V32 are tied to each other and suppressor and cathode of V32 are tied to each other. The output of inverter V33b appears on the grid of control amplifier V32` and is compared with a constant plus 75 volts on the cathode of control amplifier V32. Output is taken from the plate of control amplifier V32 and applied to the grid of variable impedance stage V33a. The plate of V33a is tied directly to the 320 volt power supply. Screen current of oscillator V29 must pass through variable impedance stage V33tr before it reaches the B+ supply.

Should the load across the high voltage power supply increase, a lower negative voltage at the contact arm of potentiometer R407 will be reflected as a positive grid potential change relative to the cathode of inverter V331?. This will result in an increased current iiow through V33!) causing the plate voltage at that tube to go down. The fall in plate voltage will be transmitted to tube V32 causing current conduction in that tube to decrease. Decreased current fiow through tube V32 will result in a higher plate voltage at that tube. This increased plate voltage will be transmitted to the grid of V33a` c-ausing the impedance of this stage to decrease, thereby effecting an increase in oscilla-tor screen voltage. This will result in higher amplitude at the primary of T401. The higher oscillations will be reflected in the secondary of T401 causing increased voltage across the bleeder comprising resistance R404, R405, R406, potentiometer R407 and resistor R408, causing the voltage at the contact arm of R407 to go up to its regulated point. A Ireduced load on the high negative voltage supply will cause a higher voltage to appear on the Contact arm of potentiometer R407. This higher voltage will be transmitted through the stabilizing circuit to again bring the voltage on the contact arm of R407 back to its regulated voltage. The advantages of the embodiment just described include compact construction, safe handling since it employs low value capacitors for filtering, delivering only a limited amount of power, easy stabilization by controlling the screen voltage of the tube oscillator, and cost comparable to that of a conventional 60-cycle per second high-voltage supply.

The tuned step up air coil transformer T401 is the basic component in the RF high voltage supply. A Miller No. 4525 oscillator coil may Ibe used here. Primary, secondary, and tickler elements `are provided. Power for the filaments of the two rectifier tubes (which may be lXZA tubes) may be obtained by ltwo single turn Iloops coupled to the tuned circuit as XZ and the loop between Y and the secondary of T401.

As heretofore explained, the frequency of oscillation is determined chieiy by the resonant frequency of the secondary winding of T401. The natural circuit capacitances that tune this winding include the distributed capacitance of the winding, the capacitance of the rectifying tubes, and the stray wiring capacitance. The primary Winding is ltuned by `a fixed 0.002 microfarad capacitor C409 to approximately the resonant frequency of the secondary. Optimum load regulation requires a coefficient of coupling between the two windings that is much greater than critical. A third yWinding of the transmission located at the end of the secondary winding opposite from the end occupied by the primary Winding isr loosely coupled to the secondary and provides good excitation for the oscillator tube (which may be a 6AQ5 tube). For efficiency, the oscillator is operated Class C. Without regulation, the rectified no load to full load voltage change is about 18%.

The stabilizing circuit for controlling the screen current of the oscillator employs an inverter (which may be one half of a 12AU7 tube), a control amplifier (which may be a lZAUG, and the other half of the l2AU7 may be used as a variable impedance stage in series with the screen grid of the oscillator. V29 is the oscillator tube. A portion of the output voltage from the high voltage negative supply is tapped from a bleeder and compared with 'a constant minus 75 volts on the cathode of the triode inverter V33b. The grid of the pentode is direct-coupled to the plate of the inverter V331) and its voltage is then compared with a constant plus 75 volts on the cathode of the control amplifier. Screen current must pass through the variable impedance stage whose grid is direct-coupled to the plate of the control amplifier. With regulation, the no load to full `load voltage change has been reduced to about 1%.

It -is thus seen that there has been provided a unique high voltage power supply suitable for use with a cathode ray tube or in equipment generally in which is required a high voltage power supply delivering voltages that are very closely regulated.

It is understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set lforth in the appended claims.

What is claimed is:

l. A power supply system comprising, in combination, first vacuum tube means including a screen grid to produce radioirequency oscillations, means for rectifying said oscillations, including a pair of output terminals for supplying thereto a rectified direct current output voltage having respective negative and positive polarities relative to zero ground potential, voltage divider means electrically connected between the negative output terminal and ground of said rectifying means and including means for selecting some intermediate voltage on said divider means, second vacuum tube means having at least an anode, control grid and a cathode, means delivering said intermediate voltage to said control grid, means connecting the negative terminal of a rst constant voltage source to said cathode, means including a load resistor connecting the positive terminal of a second constant voltage source to said anode, further vacuum tube means including a variable impedance stage and a control amplifier having the cathode of the former connected to said screen grid and the cathode of the latter connected to the positive terminal of said first constant voltage source, said further vacuum tube means being responsive to the voltage on said second vacuum tube anode for controlling the output of said first vacuum tube means to maintain said direct current output voltage at a predetermined value.

2. A power supply system comprising, in combination, first vacuum tube means including a screen grid to produce radio-frequency oscillations, means for rectifying said oscillations, including a pair of output terminals for supplying thereto a rectified direct current output voltage having respective positive and negative polarities relative to zero ground potential, voltage divider means electrically connected between the negative output terminal and ground of said rectifier means and including means for selecting some intermediate voltage on said divider means, second vacuum tube means having at least an anode, control grid, and a cathode, means delivering said intermediate voltage to said control grid, means connecting the negative terminal of a first constant voltage source to said cathode, means including a load resistor connectassigne ing the positive terminal oi a second constant voltage source to said anode, further vacuum tube means including a variable impedance stage and a control amplifier, each provided with at least an anode, a cathode and a control grid, means connecting the anode of said second vacuum tube means with the control grid of said control amplifier, means connecting the cathode of said pentode diliierence ampliier to the positive terminal of said iirst constant voltage source, means connecting the positive terminal of said second constant voltage source to said control ampliiier anode through a load resistor, means also connecting the anode of said control amplifier to the control grid of said variable impedance stage, and means connecting the cathode of said variable impedance stage to the screen grid of said rst vacuum tube means in order to maintain said direct current output voltage at a predetermined value.

3. A regulated high voltage power supply comprising, in combination, oscillator means including a multi-grid stage having a screen grid and a resonant load for producing radio-frequency oscillations, said resonant load including a radio-frequency transformer having a primary and a secondary winding of predetermined turns ratio operable to step-11p said radio-frequency oscillations to a relatively high voltage level, including a tickler winding and a pair of relatively low voltage heater windings, voltage doubler rectifier means operably electrically connected to said secondary winding of said transformer for rectifying the radio-frequency oscillations including a pair of high voltage output terminals for supplying thereto a rectified direct current high voltage output of respective negative and positive polarity relative to zero ground potential, said voltage doubler rectier means including a pair of diodes each having a filamentous cathode electrically connected to respective heater windings of said transformer, resistive bleeder means including a potentiometer in series therewith electrically connected between the negative high voltage output terminal and ground of said rectifier means, inverter means including a substantially resistive impedance responsive to incremental potential luctuations occurring in said resistive bleeder means, said inverter means including at least a triode stage having a control grid connected to said potentiometer, a cathode connected to a constant negative potential source, and an anode connected to a positive potential source through said resistive impedance, a capacitor connected between the control grid and the anode of the triode stage of said inverter means, control ampliier means directly coupled through a conductive connection to said inverter means, and variable impedance means including at least a triode stage responsive to the control amplifier means to effect a variable impedance proportional to the incremental potential fluctuations, the triode stage of the variable impedance means being electrically operably connected in series with the screen grid of said oscillator means and the positive potential source to control the amplitude of said radio-frequency oscillations, thereby regulating the direct current high voltage output of said power supply.

4. A regulated high voltage power supply comprising, in combination, oscillator means including a multigrid stage having a screen grid and a resonant load for producing radio-frequency oscillations, said resonant load including a radio-frequency transformer having a primary and a secondary winding of predetermined turns ratio operable to step-up said radio-frequency oscillations to relatively high voltage level, including a tickler winding and at least one relatively low voltage heater winding, rectiiier means operably electrically connected to said transformer for rectit'ying said radio-frequency oscillations including a pair of output terminals `for supplying thereto a rectied direct current high voltage output of respective negative and positive polarity relative to zero ground potentiai, said rectifier means including at least one diode having a iilamentous cathode electrically connected to the heater winding or said transformer, resistive bleeder means including a potentiometer in series therewith electrically connected between the negative output terminal and ground of said rectifier means, inverter means eiectrically connected to the potentiometer for response to incremental potential fluctuations occurring in said resistive bleeder means, control amplilier means responsive to the potential iiuctuations of said inverter means, and means inciuding at least a triode stage responsive to the control amplifier means to eiect a variable impedance proportional to the incremental potential iiuctuations, said triode stage being electrically operably connected in series with the screen grid of said oscillator means and a positive potential source to control the amplitude of said radio-frequency oscillations, thereby regulating the direct current high voltage output of said power supply.

5. A regulated high voltage power supply comprising, in combination, osc'dlator means including a multigrid stage having a screen grid and a resonant load for producing radio-frequency oscillations, said resonant load including a radio-frequency transformer having a primary and a secondary winding of predetermined turns ratio operable to step-up said radio-frequency oscillations to a relatively high voltage level, including a ticlder winding and a pair of relatively low voltage heater windings, voltage doubler rectifier means operably electrically connected to said transformer for rectifying the radio-frequency oscillations including a pair of output terminals for supplying thereto a rectitied direct current high voltage output of respective negative and positive polarity relative to zero ground potential, said voltage doubler rectifier means including a pair of diodes each having filamentous cathodes electrically connected to respective heater windings of said transformer, resistive bleeder means including a potentiometer in series therewith electrically connected between ground and the negative output terminal of said voltage doubler rectiier means, inverter means electrically connected to the potentiometer for response to incremental potential fluctuations occurring in said resistive bleeder means, control amplifier means responsive to the potential luctuations of said inverter means, and means including at least a triode stage responsive to the control amplilier means to effect a variable impedance proportional to the incremental potential variations, said triode stage being electrically operably connected in series with the screen grid of said oscillator means and a positive potential source to control the amplitude of said radio-frequency oscillations, thereby regulating the direct current high voltage output of said power supply.

References Cited in the file of this patent UNITED STATES PATENTS 2,215,175 Fewings Sept. 17, 1940 2,565,621 Olson Aug. 28, 1951 2,683,852 Sampson July 13, 1954 2,690,534 Kurshan Sept. 28, 1954 2,697,798 Schlesinger Dec. 11, 1954 2,720,622 Deuser Oct. 11, 1955 2,739,191 Wisenbaker et al. Mar. 20, 1956 2,753,509 Merriam July 3, 1956 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent Nog 2,894,196 July 7, i959 Lester M., Bernbaum It is hereby certified that error appears in J{she-printed specification of the above numbered patentl requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line l, for "mission" read former line ll, for "lZAU," reed 12AU6) column 5, line '7, strike out pentode";

line 8, for "differencen read -H- control Signed and sealed this 19th day of April 1960,

(SEAL) Attest:

KARL Hn AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent Nog 2,894,196

July 7, 1959 Lester M. Bernbaum It is hereby certified that error appears in the-printed specification of' the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Signed and sealed this 19th day of April 196C).A

(SEAT) Attest:

KARL H., AXLINE Attestingy Officer ROBERT C. WATSON Commissioner of Patents 

